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Old 14th July 2005, 01:33 PM   #1
skobo is offline skobo  Yugoslavia
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Default help with preamplifier

I have an old guitar amp with four 2N3055 transistors, but i dont have a preamplifier for it. So i wanted to built a preamplifier for it. I attached a schematic of the preamp i want to build. Is this a good idea? If anyone have any suggestions please tell me
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Old 14th July 2005, 04:07 PM   #2
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Looks like a standard op amp circuit. It will sure work, but i'm little unsure about the passive filter. Then if not the input impedance on you power amp is very low i think you can skip the emitter following transistor. If you want to make it really easy you can skip the whole second op. I built a preamp for a bass amp with just one input/preamping op then an active filter . Works fine
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Old 14th July 2005, 04:25 PM   #3
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No, you can only skip the emitter follower output if the input impdance of the power amp is very high.
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Old 14th July 2005, 05:06 PM   #4
sam9 is offline sam9  United States
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Yes it's a good circuit.

However, it also carries the ESP logo. Rod Elliott holds the copyright. You should get his permission by before posting the image here.

Virtually everyone on this forum is familiar with ESP so you could simply refer to the project number and thus avoid any concerns about posting copyrighted materials.
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Old 14th July 2005, 07:11 PM   #5
edl is offline edl  Hungary
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project27
project27b
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Old 15th July 2005, 12:43 AM   #6
asc is offline asc  United States
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I'm considering building a double opamp based preamp for a bass guitar. I've seen many different suggestions for the actual opamp chip. What can I use to differentiate them?


-ASC
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Old 15th July 2005, 01:50 AM   #7
skobo is offline skobo  Yugoslavia
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edl thanks for the links

the preamp that i wanted to use is actully the preamp from project 27. It says that input sensitivity of amplifier must be about 750mV for full output! How can I know what is the input sensitivity of the amp I have?
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Old 15th July 2005, 12:02 PM   #8
skobo is offline skobo  Yugoslavia
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One more thing the power suply of the amp is 2x80V how can i reduce this voltage to 15 V that i need for preamp? Can I use the original schematic that is given with preamp, and what changes should i make?
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Old 15th July 2005, 12:11 PM   #9
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The opamp takes very little current so you can use a zenerdiod to stabilize the voltage. Put a 15V 1W zener in series with 3.3K 2W (or more) resistor

edit: Yes you can use the circuit; Just change the resistor to 3.3K at least 2W.
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Old 15th July 2005, 12:54 PM   #10
jaycee is offline jaycee  United Kingdom
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Rod Elliot has a "pre-regulator" project on his site designed just for this purpose.
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